As many as a dozen Secret Service agents at the Summit of the Americas in Colombia are replaced. An incident involving a prostitute and at least one of the agents is reported.

A vehicle carrying President Obama travels through the streets of Cartagena,… (Mauricio Duenas / EPA )

CARTAGENA, Colombia — As many as a dozen Secret Service agents have been sent home from the Summit of the Americas here this weekend because of allegations of "misconduct," U.S. officials said late Friday.

The agents were relieved of duty at the summit and replaced with new agents, according to a Secret Service spokesman.

The activities that resulted in the sudden transfer of agents took place prior to President Obama's arrival in Colombia on Friday afternoon, according to sources familiar with the matter.

The incident involved suspicion of involvement with a prostitute by at least one of the agents, according to the Washington Post, which along with the Associated Press first reported the story Friday evening.

The Secret Service has opened an investigation, but spokesman Ed Donovan declined to disclose the nature of the investigation and would not confirm or deny the allegations that one or more agents were soliciting prostitutes.

One official said the Secret Service often "over-visas" for the foreign trips, bringing along more personnel than protocol dictates in the event someone gets sick or becomes incapacitated.

The matter is being handled by the Secret Service's Office of Professional Responsibility, its internal affairs division.

Although Colombia permits prostitution in certain "tolerance" areas, its solicitation would be considered inappropriate at all times by the Secret Service.

Several of the agents involved in the incident are married, according to the Post.

Secret Service agents have the responsibility of providing protection for the president at home and when he travels. Donovan said Obama's safety was never in danger.

"These personnel changes will not affect the comprehensive security plan that has been prepared in advance of the president's trip,"¿ Donovan said.

The administration had been trumpeting the progress in Latin America toward improving governance, with particular emphasis on the host country.

Obama hopes to promote that cause during meetings beginning Saturday and continuing through Sunday.